The present invention relates to an engine system, which includes a cylinder, an exhaust flow part where exhaust gas generated within the cylinder flows, and a purifying system provided to the exhaust flow part and for purifying the exhaust gas.
Conventionally, in engine systems, water is injected into cylinders in order to improve fuel efficiency, etc. In other words, by injecting water into the cylinders, the water, in addition to a combustion gas, is able to function as an operation gas to progress an expansion stroke. Thus, a combustion gas amount, furthermore an amount of fuel supplied into the cylinders can be reduced.
For example, JP5045569B discloses an engine system which includes a heat exchanger and a condenser provided at a position of an exhaust passage downstream of a purifying system in this order from the upstream side, condenses water within the exhaust gas in the exhaust passage by the condenser, increases this water in temperature by the heat exchanger using an energy of the exhaust gas, and then injects it into the cylinders. Thus, with this engine system, energy efficiency of the system as a whole can be improved.
For engine systems, in addition to an improvement in fuel efficiency, an improvement in exhaust emission performance is desired, and also purifying performance of a purifying system provided in an exhaust passage is desired to be kept high. In this regard, with the engine system of JP5045569B, the heat exchanger is provided at a position of the exhaust passage downstream of the purifying system, the exhaust gas discharged from the engine body flows into the purifying system as-is, and the temperature of the exhaust gas is not reduced by the heat exchanger until it passes through the purifying system. Therefore, when the exhaust gas at a high temperature is discharged from the engine body, the purifying system deteriorates due to the high-temperature exhaust gas and the purifying performance may degrade.